I think I have water in the fuel

Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.

VIKING_MECHANIC

GMT 400 obsessed Swede.
Joined
Jul 12, 2020
Messages
853
Reaction score
1,755
Location
Arkansas
I was driving to work this morning while it was raining pretty hard. I hit a fairly large puddle of water thanks the limited sight distance. Immediately after driving through it, my truck started to run very rough and does not want to accelerate, even with the pedal to the floor. If i come to a stop it will idle smooth for a few seconds, then it starts idle roughly and wants to die.

I first thought it was timing related and maybe got water on/under the distributor cap somehow. I got home and put my glorified diagnostic computer(it shows codes and some live data) on it and saw that the timing was sittting where it should be, around 22-25 degrees advanced. But I did notice that the SHRTFT1 is at -30.5 and the LONGFT1 is at -18. Ever since I've had the GDC, it's always showed 0 for the shrtft1 and longft1 whenever I would view the live data.

Some of the live data it is capable of showing me, I'm still trying to understand what it means and how I can use it to diagnose something, so bear with me on that.

I was planning on changing my fuel filter this weekend anyway since it's due for a change, but I don't know if that will help with the water. I imagine that I may have to drain the tank and possibly replace the pump?

Here are some screen shots of the short and long fuel trims it was showing me. 1997 C1500 5.7

This is starting the engine after it's been off for a few minutes.
You must be registered for see images attach


This is a few minutes after it's been running.
You must be registered for see images attach
 

stutaeng

I'm Awesome
Joined
Aug 7, 2019
Messages
3,410
Reaction score
4,348
Location
Dallas, TX
Definitely running rich on that 1 bank. Is bank 2 okay?

I can't visualize how water could get inside your tank, unless you drove in through like 3' of standing water. I suppose water could get into the EVAP system under your hood, but again everything is pretty high off the ground.

I'm not sure if you did have water what effect that would cause on fuel trims... probably the opposite of running rich, no?
 
Last edited:

Erik the Awful

Supporting Member
Supporting Member
Joined
Aug 9, 2019
Messages
7,610
Reaction score
15,520
Location
Choctaw, OK
You can't clean the water out of the distributor with a scan tool. Take the cap off and dry everything well. Splashing through a puddle should not put water in your tank, but if your filter's due, go ahead and replace it.

If you do have water in your tank, it will be at the bottom. While you're changing your filter, take the line loose and pump some fuel into a jug so you can see for sure if you have water in there.
 

kennythewelder

Officially Retired, B31-3 (6-G) certified welder.
Staff member
Super Moderator
Joined
Jul 14, 2014
Messages
6,496
Reaction score
9,087
Location
Louisiana
Back in 1999, I bought my first GMT 400. A Wt with a 4.3, and a 4L60E. Got it from a car lot and the owner of the lot said it needed a fuel pump. It ran, but would die out from time to time. Test drove the truck. It ran grate. Got it for $3200. Keep it for 10 years. It did however die out, mostly when stopping, but would start rite back up, and run good, untill it would do it again. Not everytime I stopped, it would die. So the lot owner had a new fuel pump that He gave me when I bought the truck. So after about a week or so, I pulled the gas tank to replace the pump. There was water in the tank. About 1/2 gallon. The fuel pump would suck a little water, and the truck would die as the water sloshed around at the bottom of the truck. Then it would pick up gas again, and run fine. Point is, water and gas don't mix. It there is water in the tank, the truck will run fine until it sucks up the water, and then the truck won't run at all. Water in the tank will not cause a miss fire.
 

stutaeng

I'm Awesome
Joined
Aug 7, 2019
Messages
3,410
Reaction score
4,348
Location
Dallas, TX
My bet is you have water in some of the electronics in the engine bay, and that's causing the ECU to be fooled. I seem to recall once I power washed my 4.3 Vortec and it acted funny and then it wouldn't start. I let it dry out completely and the problem went away.

Check your air filter box for any water. Maybe clean your MAF.

Do you have a P0172 code with those fuel trims? Any other codes?
 

VIKING_MECHANIC

GMT 400 obsessed Swede.
Joined
Jul 12, 2020
Messages
853
Reaction score
1,755
Location
Arkansas
Definitely running rich on that 1 bank. Is bank 2 okay?

I can't visualize how water could get inside your tank, unless you drove in through like 3' of standing water. I suppose water could get into the EVAP system under your hood, but again everything is pretty high off the ground.

I'm not sure if you did have water what effect that would cause on fuel trims... probably the opposite of running rich, no?
Bank 2 was the same when I took that picture. This engine runs rich mainly because of a worn out EVAP system.
 

VIKING_MECHANIC

GMT 400 obsessed Swede.
Joined
Jul 12, 2020
Messages
853
Reaction score
1,755
Location
Arkansas
You can't clean the water out of the distributor with a scan tool. Take the cap off and dry everything well. Splashing through a puddle should not put water in your tank, but if your filter's due, go ahead and replace it.

If you do have water in your tank, it will be at the bottom. While you're changing your filter, take the line loose and pump some fuel into a jug so you can see for sure if you have water in there.
The truck runs alot better now since it's has been really warm the last several hours. I'm thinking some sort of electronic got wet and was messin' with the ECU.

It definitely wasn't a puddle. This was a part of the road that doesn't typically get standing water. Today I guess it was overwhelmed. When I hit it, I was going about 30 and the splash went well over my truck. A filter change is still in order though.
 

VIKING_MECHANIC

GMT 400 obsessed Swede.
Joined
Jul 12, 2020
Messages
853
Reaction score
1,755
Location
Arkansas
My bet is you have water in some of the electronics in the engine bay, and that's causing the ECU to be fooled. I seem to recall once I power washed my 4.3 Vortec and it acted funny and then it wouldn't start. I let it dry out completely and the problem went away.

Check your air filter box for any water. Maybe clean your MAF.

Do you have a P0172 code with those fuel trims? Any other codes?
I think you are right about the electronics. After sitting for several hours, the truck runs alot better and is very responsive to throttle input. I had some water in the bottom of the air box because I left it off after working on it on Saturday. Weirdly, the filter was dry as a bone.

I didn't have that code, but I did have P0307. After sitting for hours in the heat, whatever electronic got wet must have dried enough for the engine to run like it should. I took it around the block and it drove great with no noticeable hiccups.
 
Top